Ink jet recording is a method of discharging ink from a fine nozzle as droplets to record letters or figures on a surface of a material to be recorded. As the ink jet recording system, there have come in practice a method of converting electric signals to mechanical signals by using an electrostrictive device to intermittently discharge ink stored in a nozzle head portion, thereby recording letters or figures on a surface of a material to be recorded, and a method of generating bubbles by rapidly heating ink stored in a nozzle head portion at a position quite close to a discharge portion to intermittently discharge the ink by cubical expansion due to the bubbles, thereby recording letters or figures on a surface of a material to be recorded.
Characteristics such as good drying of printing, no blur in printing, uniform printing on surfaces of all materials to be recorded and no mixing of colors in the case of multi-color printing have been required for the ink used in such ink jet printing. It particularly comes into question herein that blurs caused by fibers different in their permeability are liable to occur when paper is used as the material to be recorded.
Accordingly, various studies have hitherto been conducted for components of the ink. As means for decreasing the surface tension for that purpose, addition of diethylene glycol monobutyl ether as described in U.S. Pat. No. 5,156,675, addition of Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), an acetylene glycol surfactant, as described in U.S. Pat. No. 5,183,502, and addition of both diethylene glycol monobutyl ether and Surfynol 465 have been studied. Diethylene glycol mono-n-butyl ether is described, for example, in U.S. Pat. No. 3,291,080. In the invention described in U.S. Pat. No. 2,083,372, it has been studied to use ethers of diethylene glycol in ink. As to the conventional ink for ink jet recording, polyglycerol is used as a detergent as described in JP-A-3-152170 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), or ethyleneoxy qroup-added polyglycerol is used as JP-A-9-328644, or ethyleneoxy group-added glycerin is used as described in JP-A-4-18465.
Further, as examples in which pigments are used, it has been studied and has come in practice that the surface tension is mainly maintained high (JP-A-4-18465) to inhibit the permeability, thereby inhibiting the wetting of ink on a surface of paper to secure printing quality, in many cases. Further, as combinations of glycol ethers and pigments, there are an example in which a pigment and triethylene glycol monomethyl ether are used as described in JP-A-56-148961, and an example in which an ether of ethylene glycol, diethylene glycol or triethylene glycol is used as described in JP-A-9-111165.
However, according to the conventional techniques, when the method of inhibiting the wetting of the ink on the surface of paper is used, the permeability of ink into paper is low, so that the ink runs on plain paper, particularly regenerated paper frequently used, and it takes a long time to dry printed matter. When continuously printed, therefore, sheets of printed paper cannot be stacked just after printing, because the ink on the printed paper is difficult to be dried. In addition, this method suffers from the problem that colors adjacent to each other are mixed to blur letters, in the case of multi-color printing.
The regenerated paper has various paper components mixed, and is a collection of components different in their rate of penetration, so that blurs are liable to occur by the difference in the rate of penetration between them. For decreasing the blurs, a process of heating paper has generally been studied. However, the heating of paper and other materials to be recorded in printing suffers from the problem that it takes a long time to elevate the temperature of a heating unit in a device to a predetermined temperature, that the consumption of electricity of a main body of a device is increased, or that paper and other materials to be recorded are damaged.
When ink containing a pigment is printed on paper having an ordinary sizing agent as a medium to be recorded, the problem is also encountered that the pigment remains on a surface of the paper unless permeability is imparted to some extent to the ink, thereby deteriorating scratch resistance. However, high surface tension limits the kind of paper for performing uniform printing, or is liable to cause deterioration of printing quality or image quality.